The present invention relates to a balloon catheter for medical application, and particularly to a dilation balloon catheter to be inserted in a body cavity such as a blood vessel, which catheter has a dilation balloon to be very easily insertable in a narrow, eccentric or meandering stenosis portion, or a branch portion in the body cavity in order to dilate the stenosis portion.
A dilation balloon catheter generally includes inner and outer tubes to be inserted in a body cavity and a cylindrical balloon connected to the inner and outer tubes.
Such a cylindrical balloon has been required to satisfy inconsistent needs for a sufficient strength to withstand a pressure for dilation of the balloon and a good trackability in a blood vessel. Specifically, the dilation balloon has been required to have a characteristic easily insertable even in a very narrow, eccentric, or meandering stenosis portion without damaging the stenosis portion while keeping a high strength to withstand pressure.
To meet these requirements, various balloons made from polymers have been proposed.
Balloon catheters made from thermoplastic polymers have been known. Examples of the thermoplastic polymers used for such balloon catheters include an ethylene-butylene-styrene block copolymer containing polyethylene, ionomer, and low molecular weight polystyrene, and further polypropylene (if needed); a derivative from the above copolymer by substituting ethylene and butylenes by butadiene or isoprene; polyvinyl chloride; polyurethane; polyester or copolyester; polyamide or polyamide elastomer; thermoplastic rubber; silicone-polycarbonate copolymer; and ethylene-vinyl acetate copolymer.
A balloon made from thermoplastic polyimide has been also proposed, for example, in Published Japanese Translation of a PCT Application No. Hei 9-507148 (WO95/18647).
However, in recent years, a balloon catheter including a balloon having a higher strength to withstand a pressure has been required.
It has been also known to use a composite material obtained by combining a resin with long-fibers (filaments) or a fiber-structure such as a woven fabric or knit fabric of the long-fibers for enhancing the strength to withstand pressure of a balloon.
For example, Published Japanese Translation of a PCT Application No. 2001-504359 (WO98/05377) has proposed a composite material used for a balloon, wherein the composite material is obtained by forming a resin integrally with long-fibers in the form of yarns or a fiber-structure such as a plain weave fabric, satin fabric, twilled fabric, basket weave fabric, braid, or winding fabric of the long-fibers. The composite material obtained by forming a resin integrally with such long-fibers or a fiber-structure of the long-fibers, however, has a disadvantage that it is generally difficult to sufficiently impregnate a gap between the adjacent single fibers in the yarn with the resin, to cause defects not impregnated with the resin. In particular, in the case of using multi-filaments, such detects not impregnated with a resin are liable to occur. Another disadvantage is that since the method disclosed in the above document requires the step of forming the fiber-structure into the shape of a balloon, if it is intended to produce a balloon having a fine diameter, the uniformity of production and the production yield may be degraded.
U.S. Ser. No. 2001/43998 has disclosed a balloon catheter including a balloon reinforced by reinforcing bodies in the form of short-fibers disposed in a matrix resin. According to the method disclosed in this document, a reinforcing resin such as total aromatic polyester forming liquid crystal in a melted state is disposed in the form of whiskers (pulp) in a matrix resin by blending the reinforcing resin with the matrix resin and simultaneously melting the reinforcing resin together with the matrix resin in an extrusion cylinder, extruding the compound from discharge nozzles of a die, to form the melted reinforcing resin into whisker-like shapes elongated in the extrusion direction by shearing orientation caused at the time of extrusion from the discharge nozzles, and solidifying the extruded product by cooling in a water bath, wherein the reinforcing resin in the form of particles before melting is disposed in the form of whiskers (pulp) in the matrix resin by shearing applied to the melted reinforcing resin. The above document has also disclosed that the reinforcing resin can be disposed in the form of whiskers by increasing the draft ratio of general extrusion molding, and further the reinforcing resin can be disposed in the form of whiskers oriented in the circumferential direction of the tubular parison to be molded into the balloon by rotating a mandrel (core) or an outer die portion of the extrusion die.
The extrusion method disclosed in the above-described document, however, has a disadvantage that since the reinforcing resin is disposed in the form of whiskers (pulp) in the matrix resin by discharging the reinforcing resin from a specific number of the discharge nozzles of the die while applying a rotational force and a shearing force to the reinforcing resin, the reinforcing resin is formed into the whiskers (pulp) extending in lines of the number corresponding to that of the discharge nozzles of the die, and accordingly, the reinforcing resin is not present among the lines of the whiskers, with a result that the reinforcing effect becomes insufficient, to simply cause pin-holes and cracks. Further, as is easily appreciated by those skilled in the art, it often fails to obtain a sufficient reinforcing effect only by discharging the melted reinforcing resin. On the other hand, it may be conceivable to improve the crystallinity of the reinforcing resin by a heat-treatment; however, such a heat-treatment must be performed at a temperature being too high to deteriorate or thermally deform the matrix resin. It may be also conceivable to use a liquid crystal resin having a chemical structure allowing the resin to be molded or crystallized at a low temperature against which the matrix resin withstands; however, such a liquid crystal resin is poor in rigidity as the reinforcing material.